Engineering plastics are excellent in mechanical properties, heat resistance, electrical properties, and the like, and have been used in various applications such as electrical/electronic equipment, home electrical appliances, and OA equipment. In recent years, in these applications, a molded body has become increasingly larger, thinner and more complex in shape, and thus, there is a demand for improvement in molding processability.
Melt flowability, melt tension, or the like is mentioned as an indicator of molding processability of the engineering plastic. When melt flowability is high, it is easy to obtain a molded body having a large size and/or a thin thickness at the time of injection molding. When melt tension is high, molding defects such as jetting at the time of injection molding and drawdown at the time of blow molding or vacuum molding are less likely to occur.
As the method of improving melt flowability at the time of molding process without impairing excellent properties (mechanical properties, heat resistance, and the like) of the engineering plastic, methods are proposed in which a powder prepared by coagulating a copolymer, which is obtained by subjecting an aromatic vinyl monomer and a phenyl methacrylate to emulsion polymerization, or a powder prepared by coagulating a copolymer, which is obtained by subjecting styrene and phenyl methacrylate to emulsion polymerization, in the presence of a copolymer, which is obtained by subjecting α-methyl styrene, styrene, and phenyl methacrylate to emulsion polymerization, is blended, as a flowability improver, in a polycarbonate resin serving as an engineering plastic (Patent Documents 1 and 2).
In addition, as the method of improving melt tension of the engineering plastic and preventing drawdown at the time of molding, methods are proposed in which a powder prepared by coagulating a high-molecular-weight acrylic polymer, which is polymerized by emulsion polymerization, is blended, as a melt tension improver, in an engineering plastic (Patent Documents 3 and 4).
However, since these flowability improver and melt tension improver have a high glass transition temperature, when a latex obtainable by emulsion polymerization is coagulated and a polymer powder is recovered, atomization of the powder or solidification failure is likely to occur. As a result, there is possibility that the powder flowability or the bulk density of the obtained powder is decreased, and thus a problem arises in improvement of powder property.
In addition, when a resin composition containing the flowability improver or the melt tension improver described above is molded at high temperature in order to achieve high melt flowability, there is a concern that foreign substances remaining in the flowability improver or the melt tension improver impair the appearance, the mechanical strength, or the like of the molded body. From this reason, in the resin composition, there is also a strong demand for improvement in thermal stability at high-temperature molding.